Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$167.40	8.294%	$181.2842	$181.28	$181.30	$181.30
Purchase #2	$224.37	10.390%	$247.682	$247.68	$247.70	$247.70
Purchase #3	$65.98	4.315%	$68.827	$68.83	$68.85	$68.80
Purchase #4	$181.45	10.318%	$200.172	$200.17	$200.15	$200.20
Purchase #5	$85.30	5.393%	$89.9002	$89.90	$89.90	$89.90
Purchase #6	$20.48	3.359%	$21.1679	$21.17	$21.15	$21.20
Purchase #7	$97.42	7.742%	$104.9623	$104.96	$104.95	$105.00
7 purchase totals =	$842.40		$913.9956	$913.99	$914.00	$914.10